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Extraction equilibria of picolinic acid from aqueous solution by tridodecylamine (TDA)
Desalination 268 (2011) 134–140
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Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Extraction equilibria of picolinic acid from aqueous solution by tridodecylamine (TDA) Amaç Fatih Tuyun, Hasan Uslu ⁎ Beykent University, Engineering & Architecture Faculty, Chemical Engineering Department, Ayazağa, İstanbul, Turkey
a r t i c l e
i n f o
Article history: Received 15 July 2010 Received in revised form 28 September 2010 Accepted 2 October 2010 Available online 5 November 2010 Keywords: Reactive extraction Picolinic acid Tridodecylamine (TDA)
a b s t r a c t Pyridine compounds having a carboxyl side chain at the 2-position are attracting considerable attention for their ability. Chromium, manganese, iron, copper, zinc, and molybdenum are present as chelating agents in the human body. Picolinic acid acts as a chelating agent instead of these elements. In this study, the extraction of picolinic acid was studied using tridodecylamine (TDA) with respect to the functional groups of the diluents. All experiments reported on the extraction of picolinic acid by tridodecylamine (TDA) dissolved in different two different acetates (ethyl acetate and propyl acetate), two different alcohols (1-octanol and 1decanol), and two different ketones (2-heptanone and 2-octanone), as well as single solvents. The C* ), experimental results of batch extraction experiments are reported as distribution coefficients, (KD = CPA PA loading factors, Z, and extraction efficiency, E. All measurements were carried out at 298.15 K. The highest distribution coefficient has been obtained by 1-octanol value of 4.121 and its extraction efficiency is 80%. Linear Solvation Energy Relationship (LSER) model has been applied to the experimental data with good regression coefficient, R2:0.90. Model results are close to experimental results. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Pyridine carboxylic acids and their derivatives are attracting considerable attention for their presence in many natural products. Especially, they are used in medicinal chemists, owing to the many of physiological facilities displayed by the natural and many synthetic derivatives [1]. They are also important from the industrial point of view; for example, in nuclear reactor decontamination, where the low oxidation state metal ion (LOMI) decontamination process uses V(II)/ V(III) picolinic acid complexes in the decontamination solutions [5,6]. 2-Pyridinecarboxylic acid, also known as picolinic acid, contains a carboxylic group in the ortho-position to the nitrogen in the pyridine ring, acting as a bidentate ligand by (N, COO−) coordination. It forms in the body as an intermediate in the tryptophan degradation pathway and it is an approved food supplement [2]. Picolinic acid contains two active groups: a carboxyl group and a pyridinic nitrogen atom, therefore its aqueous solutions are weakly acidic. When the product must be concentrated from an aqueous solution, existing fermentation technologies for large-scale production of common chemical feedstocks are not ready for action with
⁎ Corresponding author. Tel.: +90 212 4441997 5274; fax: +90 212 8675066. E-mail address: [email protected] (H. Uslu). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.10.009
traditional processes. These processes are expensive because of highenergy consumption occupied. To improve the biological production of picolinic acid and its derivatives by fermentation, it is necessary to develop new methods that reduce the charge of the recovery steps. Therefore, a realistic and more capable method using cheap and environment friendly is still of attention [3,4]. Physical extraction with pure organic solvents not containing amine- and phosphorus-structured extractant has been verified unsuitable for the recovery of organic acids. Because organic acids have high affinity to water, it gives low distribution coefficients. The pure diluents do not extract the solute, while the modifier influences the extracting power of the amine. When the amine salts with carboxylic acids are slightly soluble in the aqueous phase, a vital role of the modifier is to improve the solubility of the salts in the extracted phase [7]. Reactive liquid–liquid extraction of the acid by a suitable extractant has been found to be a promising alternative to conventional processes. Several authors [8–10] have studied the recovery of carboxylic acids by liquid–liquid extraction with aliphatic tertiary amines dissolved in organic diluents. The behavior and base strength of various amine types and classes in the reactive extraction of hydrochloric acid in toluene diluents have been investigated [11]. It is noteworthy in a study that the base strength increased in the order: tertiary amine N secondary amine N primary amine. Extraction of carboxyl acids by using some aliphatic amines and gel have been used successfully and some of reports could be found in the literature hitherto [12–28].
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140
where a denotes the activity. Replacing the activities by the products of molalities and molal activity coefficients, γ, gives Eq. (3).
Picolinic Acid O
C
O
O
H
C
H O
HO
C
Structure I
O K=
Structure II
Structure III
Table 1 Results of physical extraction of picolinic acid with pure solvents.
Ketones Alcohols
ð3Þ
3
In Eq. (3), mHA is the molality of acid, m*R3N is the molality of amine, γPA is the molal activity coefficient of acid, γ*R3N is the molal activity coefficient of amine, γ*(PA).(R3N) is the molal the activity coefficient of the complex, m*(PA).(R3N) is the molality of complex. The loading of the extractant (Z) is defined as the total concentration of acid in the organic phase divided by the total concentration of amine in the organic phase [8]. The expression for Z can be written in the form
Fig. 1. Structures of picolinic acid.
Esters
m*ðPAÞ:ðR NÞ ⋅γ*ðPAÞ:ðR NÞ 3 3 ðmPA ⋅γPA Þ⋅ m*R N ⋅γ*R N 3
N
N
N
135
T
T
Z = CPA = CTDA :
Solvents
pHaq.
C⁎PA (mol dm− 3)
KD
E
Ethyl acetate Propyl acetate 2-Heptanone 2-Octanone 1-Octanol 1-Decanol
3.154 3.131 3.097 3.084 3.084 3.126
0.044 0.057 0.012 0.032 0.062 0.057
0.059 0.077 0.016 0.041 0.084 0.077
5.565 7.145 1.535 3.981 7.751 7.145
ð4Þ
⁎ is total concentration of acid in the organic phase, In Eq. (4), CPA ⁎ mol/L and CTDA is the total concentration of amine in the organic phase. The partitioning coefficients, KD, for picolinic acid extracted from water into the organic phase were determined by T
KD = CPA = CPA :
ð5Þ
The efficiency of extraction, E, is expressed as 2. Theory
E = ½1−ðCPA = CPA0 Þ:100
The extraction of picolinic acid (HA) with tridodecylamine (R3N) can be described by the following reaction [8,10].
where CPA is the concentration of acid in the aqueous phase after extraction and CPA0 is the initial concentration of acid in the aqueous phase.
ð1Þ
PA + R3 N↔ðPAÞ:ðR3 NÞ
In Eq. (1) PA represents the nondissociated part of the acid present in the aqueous phase and the organic phase species are marked with an asterisk (*). Reaction (1) can be characterized by the overall thermodynamic extraction constant K. a*ðPAÞ:ðR
3 NÞ
aPA ⋅a*R
ð2Þ
3N
3. Materials and experimental procedure 3.1. Materials TDA (M = 521.98 g mol−1) (purity N 99 wt.%), picolinic acid (purity N 98 wt.%) and the solvents were purchased from Merck Co., (Darmstadt, Germany). All chemicals were used without further purification. Alcohols (1-octanol and 1-decanol), ketones (2-heptanones and 2-octanone), and esters (ethyl acetate and propyl acetate) (purities N 99 wt.%) were supplied from Merck and Fluka.
0,090 1-Octanol
0,080
Propyl Acetate
1-Decanol
0,070
Distribution Coefficients
K=
ð6Þ
0,060
Ethyl Acetate
0,050 2-Octanone
0,040 0,030 0,020
2-Heptanone
0,010 0,000 Fig. 2. Distribution coefficients of picolinic acid between water and solvents used in this study.
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Table 2 Results of extraction of picolinic acid with TDA + ester systems. Solvents (esters)
C⁎TDA (mol dm− 3)
pHaq.
C⁎PA (mol dm− 3)
KD
Z
E
Ethyl acetate
0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785
3.772 3.840 3.917 3.923 3.926 3.588 3.714 3.762 3.767 3.775 3.703 3.887 4.107 4.334 4.349 3.742 3.762 4.108 4.217 4.299 3.550 3.632 3.820 3.823 3.826 3.504 3.682 3.713 3.768 3.771
0.183 0.292 0.345 0.357 0.370 0.140 0.200 0.243 0.254 0.264 0.160 0.336 0.492 0.617 0.641 0.214 0.300 0.478 0.522 0.564 0.138 0.210 0.269 0.304 0.316 0.082 0.154 0.221 0.241 0.259
0.298 0.579 0.764 0.811 0.868 0.214 0.334 0.440 0.467 0.495 0.252 0.729 1.612 3.423 4.121 0.366 0.602 1.498 1.902 2.419 0.210 0.358 0.510 0.617 0.657 0.115 0.239 0.384 0.433 0.482
1.164 0.931 0.733 0.568 0.472 0.894 0.636 0.517 0.404 0.336 1.020 1.070 1.044 0.982 0.817 1.361 0.954 1.015 0.832 0.718 0.881 0.669 0.572 0.484 0.403 0.522 0.489 0.470 0.383 0.330
22.934 36.673 43.301 44.775 46.472 17.602 25.052 30.545 31.823 33.097 20.096 42.164 61.720 77.393 80.472 26.811 37.592 59.961 65.546 70.749 17.364 26.343 33.791 38.166 39.654 10.291 19.266 27.747 30.196 32.518
Propyl acetate
1-Octanol
1-Decanol
2-Heptanone
2-Octanone
3.2. Experimental procedure
4. Results and discussion
Extraction experiments involve shaking equal volumes (20 ml) of aqueous and organic phases for 6 h in a temperature controlled shaker (GFL) at 25 °C and 40 rpm speed, followed by settling of the mixture for at least 2 h at the same temperature in incubator. 6 h was found as sufficient time for the attainment of equilibrium in preliminary tests. Aqueous phase pH was measured by a (Mettler Toledo) pH meter. Aqueous solutions of picolinic acid have pH values in the range from 3.084 to 4.349. Aqueous-phase acid concentration was determined by titration of 0.1 N NaOH. Relative uncertainty of aqueous phase determination was not exceeding ±3%. The acid content in the organic phase was determined with a mass balance.
The picolinic acid monomer can exist in three conformations. From the relative energies gathered (Fig. 1), it is evident that the structure of picolinic acid is the most stable one which able to make a complex with amine via intramolecular hydrogen bond occurred between carboxylic acid and TDA (COOH⋯N). The other two are less stable by 3.50 and 3.67 kcal/mol, respectively, whereas structure I is the most stable one with 0.00 energy difference [28]. The physical extraction of picolinic acid was studied for better understanding of the amine effect on picolinic acid (reactive extraction). Table 1 presents and Fig. 2 shows the extraction of picolinic acid by pure solvents without TDA. With the help of pure 1-octanol the highest
4,5
Distribution Coefficients
4,0 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0 0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 3. Variation of distribution coefficients with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140
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1,4 1,3 1,2
Loading Factor
1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 4. Variation of loading factor with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
90,000 80,000
Extraction Efficiency
70,000 60,000 50,000 40,000 30,000 20,000 10,000 0,000 0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 5. Variation of extraction efficiency with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
4,0000
Distribution Coefficients
3,5000 3,0000 2,5000 2,0000 1,5000 1,0000 0,5000 3,4000
3,5000
3,6000
3,7000
3,8000
3,9000
4,0000
4,1000
4,2000
4,3000
4,4000
pH Fig. 6. Variation of distribution coefficiency with pH in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
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Fig. 7. FTIR analysis of organic phase and TDA.
extraction degree was raised to 7.751% of picolinic acid in aqueous phase to organic phase. In the diluents categories, alcohols more dominated than others did since they have high polarity. The extraction of picolinic acid by TDA dissolved in alcohols (1-octanol and 1-decanol), ketones (2heptanone and 2-octanone), and esters (ethyl acetate and propyl acetate) was studied. Results of the equilibrium data on the reactive extraction of picolinic acid from aqueous phase to organic phase are presented in Table 2. The prepared constant concentrations of TDA in various solvents were between 0.157 mol dm−3 and 0.785 mol dm−3. The picolinic acid concentration in the initial aqueous phase was 0.797 mol dm−3. According to Table 2 and Fig. 3, the distribution coefficient for picolinic acid extraction with TDA was obtained obviously by the following orders: In alcohols: 1-octanol N 1-decanol In esters: ethyl acetate N propyl acetate In ketones: 2-heptanone N 2-octanone.
As has been obviously seen from Fig. 4 in contrast to action of KD values, the loading factors show gradual decrease when increasing amine concentration in the organic phase. In low concentrations (interval 0.157 mol dm−3–0.471 mol dm−3) over loadings (Z N 1) were observed. As per Wasewar et al. [21]. If 1 N Z N 0.5 complex formation (2 acid molecules + 1 amine molecule) ½TDA : ACID + ½ACID↔½TDA : 2ACIDS If Z N 1 (3 acid molecules + 1 amine molecule) can be considered ½TDA : 2ACID + ½ACID↔½TDA : 3ACIDS: Fig. 5 demonstrates the extraction efficiency of TDA–diluents mixture changes when increasing initial concentration of TDA in organic phase. The highest extraction efficiency of picolinic acid has been found as 80.472% using 1-octanol at 0.785 mol dm−3 initial
Table 3 Solvatochromic parameters for alcohols [32,35,36]. Solvents
π*
δ
β
α
Octan-1-ol Decan-1-ol Propyl acetate Ethyl acetate 2-Heptanone
0.40 0.40 0.53 0.55 0.61
0 0 0 0 0
0.81 0.81 0.45 0.45 0.48
0.77 0.72 0 0 0
Table 4 Results of regression coefficient for LSER equation. Coefficients
K0D
s
d
b
a
R2
− 1.337
− 4.451
0
6.842
2.301
0.90
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140 Table 5 KD values for the experimental and LSER model. Solvents (ketones)
C⁎TDA (mol dm− 3)
KD
KDmodel
2-Heptanone
0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785
0.210 0.358 0.510 0.617 0.657 0.252 0.729 1.612 3.423 4.121 0.366 0.602 1.498 1.902 2.419 0.298 0.579 0.764 0.811 0.868 0.214 0.334 0.440 0.467 0.495
0.225 0.375 0.468 0.641 0.644 0.266 0.741 1.645 3.877 3.997 0.372 0.605 1.559 2.055 2.657 0.325 0.566 0.771 0.955 0.965 0.311 0.335 0.554 0.565 0.585
Octanol
Decanol
Ethyl acetate
Propyl acetate
concentration of TDA. The acid concentration in the organic phase at equilibrium C⁎PA increases from 0.082 mol dm−3 to 0.641 mol dm−3 with increasing concentration of TDA from 0.157 mol dm−3 to 0.785 mol dm−3. Distribution coefficient has increased from 0.016 to 4.121 with increasing initial TDA concentration among the all diluents used in this study in Fig. 6. Obviously, as can be seen from Table 2, the increase of amine concentration brings about gradual increase of extraction efficiency. At 0.785 mol dm−3, the maximum values of 80.472% and 70.749% of the picolinic acid (for two diluents) are extracted with 1-octanol and 1-decanol, respectively. The equilibrium data about distribution of picolinic acid between water and TDA dissolved in 2-heptanone and 2-octanone were presented in Table 2. It was found that the extraction power of TDA is more effective in the presence of 2-heptanone than 2-octanone. The most characteristic bands in the FTIR spectra of organic phase (bottom, after extraction) and amine (top, before extraction) (Fig. 7)
139
should be mentioned that correspond to the stretching vibrations of carbonyl group in the expected regions. It is often used here to correlate the IR spectrum with the carboxylate structures by using the difference between the asymmetric and symmetric carboxylate stretches. This value has been observed at 1609 cm−1 for stretching vibrations of carbonyl group. In the spectral range over 3000 cm−1, at 3350 cm−1, O–H stretch has occurred at organic phase. Tridodecylamine is a tertiary amine so that N–H stretch has not been observed at 3300–3000 cm−1, or an N–H wag. The C–N stretch has been seen at 1378 cm−1 (non-aromatic) at amine. A LSER approach was introduced by Kamlet and Taft [29] and then improved by Abraham [30]. It characterizes solvation effects in terms of nonspecific and hydrogen bonding interactions. Thus, a solvation property of interest (XYZ) for an organic solute is modeled by a linear solvation energy relationship of the form [31] 0
XYZ = XYZ + s π* + sdδ + bβ + aα:
ð7Þ
In Eq. (7), π* and δ are the solvatochromic parameters that measure dipole + dipole and dipole + induced dipole interactions, respectively. The solvatochromic parameter α scale of solvent HBD (hydrogen-bond donor) acidities describes the ability of the solvent to donate a proton in a solvent to solute hydrogen bond. The β scale of HBA (hydrogen-bond acceptor) basicities provides a measure of the solvent's ability to accept a proton (donate an electron pair) in a solute to solvent hydrogen bond, respectively. The coefficients s, d, a and b include the properties of solute coming from regression [32]. As mentioned in Uslu's previous studies [33,34] the general form of LSER (Eq. (5)) can be rearranged to predict distribution coefficient of reactive extraction systems, 0
ln KD = ln KD + sðπ* + dδÞ + bβ + aα:
The solvatochromic parameters (π*, δ, β, and α) for each solvent were taken from the literature and shown in Table 3. The results of the regression of data obtained from experimental data according to Eq. (8) give other coefficients (K0D, s, d, a and b) and their values were presented in Table 4. These values give us the new equation to predict distribution coefficients for these extraction systems and comparison of KD values between calculated and experimental was given in Table 5. It has been seen clearly from Fig. 8 that the predicted values of KD are close to experimental data. This situation shows that the LSER
4.5 4
KD Experimental
3.5 3 2.5 2 1.5 1 0.5 0
0
1
2
ð8Þ
3
4
KD LSER model Fig. 8. Comparison of KD values between experimental and LSER model.
5
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model is in good agreement with experimental data in these conditions. For the suitability of the data, the root-mean-square deviation (RMSD) values are calculated from the difference between the experimental data and the predictions of the LSER model, according to the following equation: RMSD =
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 n ∑ KD −KDmodel N i=1
ð9Þ
where KD, is the experimental distribution coefficient and Kmodel is the D calculated distribution coefficient. N is the number of experimental data. The RMSD value of LSER model is determined to be 0.89. The RMSD value shows that all predicted distribution coefficients agree well with each other, and also the agreements between predictions and measurements are acceptable, considering experimental uncertainty. 5. Conclusion The reactive extraction of picolinic acid by using TDA dissolved in three diluents was investigated. The distribution coefficients, loading factors, and extraction efficiencies were obtained for this extraction system. The highest synergistic extraction efficiency was found for TDA + 1-octanol extractant system with KD value of 4.121. Polar diluents have been shown to be more convenient diluents than inert ones (nonpolar), due to their higher distribution. However, active polar and proton-donating diluents such as alcohols have been shown to be the most suitable diluents for amines because they give the highest distributions resulting from the formation of solvates through specific hydrogen bonding between the proton of the diluents and the acid–amine complex. The employment of the reactive extraction method on recovery steps after production of acids provides us the solutions of some problems such as high-energy consumption, tedious work up procedures, cost, and environment problems. References [1] K.A. Idriss, M.S. Saleh, H. Sedaira, M.M. Seleim, E.Y. Hashem, Solution equilibria and stability of the complexes of pyridinecarboxylic acids — complexation reaction of mercury(II) with 2-hydroxynicotinic acid, Monatsh. Chem. 122 (1991) 507–520. [2] RA. Anderson, Chromium in the prevention and control of diabetes, Diabetes Metab. 26 (2000) 22. [3] L.R. Wang, Y. Fang, UV-Raman study and theoretical analogue of picolinic acid in aqueous solution, J. Molec. Spect. 234 (2005) 137–142. [4] J.M. González-Sáiz, M.A. Fernández-Torroba, C. Pizarro, Application of weakly basic copolymer polyacrylamide (acrylamide-co-N,N,'-dimethylaminoethyl methacrylate) gels in the recovery of citric acid, Euro. Poly. J. 33 (1997) 475–485. [5] C.G. Pope, E. Matijecic, R.C. Pate, Adsorption of nicotinic, picolinic, and dipicolinic acids on monodispersed sols of alpha-Fe2O3 and Cr(OH)3, J. Colloid Interface Sci. 80 (1981) 74–83. [6] A.M. Lannon, A.G. Lappin, M.G. Segal, Electron-transfer reactions of tris (picolinato) vanadate(II), a LOMI reagent, Inorg. Chem. 23 (1984) 4167. [7] D.S. Yankov, J.R. Molinier, G.D. Kyuchoukov, Extraction of tartaric acid by trioctylamine, Bulg. Chem. Comm. 31 (1999) 446. [8] V. Bizek, J. Horacek, R. Rericha, M. Kousova, Amine extraction of hydroxycarboxylic acids 1. Extraction of citric-acid with 1-octanol n-heptane solutions of trialkylamine, Ind. Eng. Chem. Res. 31 (1992) 1554–1562. [9] R.S. Juang, R.H. Huang, Equilibrium studies on reactive extraction of lactic acid with an amine extractant, Chem. Eng. J. 65 (1997) 47–53. [10] A.S. Kertes, C.J. King, Extraction chemistry of fermentation product carboxylic acids, J. Biotechnol. Bioeng. 28 (1986) 269–282. [11] R.R. Grinstead, Proc. of the Int. Solvent Extraction Conf. North-Holland, Amsterdam, 1967. [12] G. Kyuchoukov, A. Labbaci, J. Albet, J. Molinier, Simultaneous influence of active and “inert” diluents on the extraction of lactic acid by means of tri-n-octylamine (TOA) and tri-iso-octylamine (TIOA), Ind. Eng. Chem. Res. 45 (2006) 503–510.
[13] Y.S. Aşçı, İ. İnci, Extraction of glycolic acid from aqueous solutions by amberlite LA2 in different diluent solvents, J. Chem. Eng. Data 54 (2009) 2791–2794. [14] Y.K. Hong, W.H. Hong, Equilibrium studies on reactive extraction of succinic acid from aqueous solutions with tertiary amines, Bioprocess. Eng. 22 (2000) 477. [15] N. Pehlivanoğlu, H. Uslu, Ş.İ. Kırbaşlar, Experimental and modeling studies on the extraction of glutaric acid by trioctylamine, J. Chem. Eng. Data 54 (2009) 3202–3207. [16] D. Cascaval, A.I. Galaction, A.C. Blaga, M. Camarut, Comparative study on reactive extraction of nicotinic acid with amberlite LA-2 and D2EHPA, Sep. Sci. Technol. 42 (2007) 389–401. [17] H. Uslu, C. Bayat, S. Gökmen, Y. Yorulmaz, Reactive extraction and LSER model consideration of lactic acid with tripropylamine plus organic solvent systems from aqueous solution at room temperature, Desalination 249 (2009) 694–698. [18] H. Uslu, Liquid plus liquid equilibria of the (water plus tartaric acid plus Alamine 336 plus organic solvents) at 298.15 K, Fluid Phase Equilib. 253 (2007) 12–18. [19] R.-S. Juang, W.-T. Huang, Equilibrium studies on the extraction of citric-acid from aqueous-solutions with tri-N-octylamine, J. Chem. Eng. Jpn 27 (1994) 498–504. [20] R.-S. Juang, Y.-S. Lin, Distribution equilibrium of penicillin G between water and organic solutions of amberlite LA-2, Chem. Eng. J. 62 (1996) 231–236. [21] K.L. Wasewar, A.A. Yawarkal, A.J. Moulijn, V.G. Pangarkar, Fermentation of glucose to lactic acid coupled with reactive extraction: a review, Ind. Eng. Chem. Res. 43 (2004) 5969. [22] K.L. Wasewar, A.B.M. Heesink, G.F. Versteeg, V.G. Pangarkar, Reactive extraction of lactic acid using alamine 336 in MIBK: equilibria and kinetics, J. Biotechnol. 97 (2002) 59. [23] H. Uslu, Ş.İ. Kırbaşlar, Solvent effects on the extraction of malic acid from aqueous solution by secondary amine extractant, Sep. Purif. Technol. 71 (2010) 22–29. [24] Y.S. Aşçı, İ. İnci, Extraction equilibria of propionic acid from aqueous solutions by amberlite LA-2 in diluent solvents, Chem. Eng. J. 155 (2009) 784–788. [25] Y.S. Aşçı, İ. İnci, Extraction equilibria of succinic acid from aqueous solutions by amberlite LA-2 in various diluents, J. Chem. Eng. Data 55 (2010) 847–851. [26] D. Cascaval, A. Galaction, C. Oniscu, Selective pertraction of carboxylic acids obtained by citric fermentation, Sep. Sci. Technol. 39 (2004) 1907–1925. [27] A. Keshav, K.L. Wasewar, S. Chand, Equilibrium and kinetics of the extraction of propionic acid using tri-n-octylphosphineoxide, Chem. Eng. Technol. 31 (2008) 1290–1295. [28] P. Koczoń, J.Cz. Dobrowolski, W. Lewandowski, A.P. Mazurek, Experimental and theoretical IR and Raman spectra of picolinic, nicotinic and isonicotinic acids, J. Mol. Struct. 655 (2003) 89–95. [29] M.J. Kamlet, J.L.M. Abboud, R.W. Taft, Linear solvation energy relationships 8. Solvent effects on NMR spectral shifts and coupling-constants, Prog. Phys. Org. Chem. 13 (1981) 485. [30] M.H. Abraham, Scales of solute hydrogen-bonding — their construction and application to physicochemical and biochemical processes, Chem. Soc. Rev. (1993) 73. [31] M.H. Abraham, J.M.R. Gola, J.E. Cometto-Muniz, W.S. Cain, The solvation properties of nitric oxide, J. Chem. Soc. Perkin Trans. 2 (2000) 2067. [32] M.J. Kamlet, M. Abboud, M.H. Abraham, R.W. Taft, Linear solvation energy relationships. 23. A comprehensive collection of the solvatochromic parameters, pi-star, alpha and beta, and some methods for simplifying the generalized solvatochromic equation, J. Org. Chem. 48 (1983) 2877–2887. [33] H. Uslu, Linear solvation energy relationship (LSER) modeling and kinetic studies on propionic acid reactive extraction using alamine 336 in a toluene solution, Ind. Eng. Chem. Res. 45 (2006) 5788. [34] H. Uslu, Ş.İ. Kırbaşlar, Extraction of aqueous of malic acid by trioctylamine extractant in various diluents, Fluid Phase Equilib. 287 (2010) 134–140. [35] D.N. Legget, Modeling solvent extraction using the solvatochromic parameters. alpha., beta., and .pi.*, Anal. Chem. 65 (1993) 2907. [36] M.J. Kamlet, R.M. Doherty, M.H. Abraham, Y. Marcus, R.E. Taft, Linear solvation energy relationships. 46. An improved equation for correlation and prediction of octanol water partition-coefficients of organic nonelectrolytes (including strong hydrogen-bond donor solutes), J. Phys. Chem. 92 (1988) 5244–5255.
Glossary Symbols and abbreviations
TDA: Tridodecylamine HA: Picolinic acid KD: Distribution coefficient Z: Loading factor CPA: Picolinic acid concentration [mol.dm-3] CPA0: Initial concentration of picolinic acid [mol dm− 3] E: Extraction efficiency Aq: Aqueous phase *: Organic phase
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Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Extraction equilibria of picolinic acid from aqueous solution by tridodecylamine (TDA) Amaç Fatih Tuyun, Hasan Uslu ⁎ Beykent University, Engineering & Architecture Faculty, Chemical Engineering Department, Ayazağa, İstanbul, Turkey
a r t i c l e
i n f o
Article history: Received 15 July 2010 Received in revised form 28 September 2010 Accepted 2 October 2010 Available online 5 November 2010 Keywords: Reactive extraction Picolinic acid Tridodecylamine (TDA)
a b s t r a c t Pyridine compounds having a carboxyl side chain at the 2-position are attracting considerable attention for their ability. Chromium, manganese, iron, copper, zinc, and molybdenum are present as chelating agents in the human body. Picolinic acid acts as a chelating agent instead of these elements. In this study, the extraction of picolinic acid was studied using tridodecylamine (TDA) with respect to the functional groups of the diluents. All experiments reported on the extraction of picolinic acid by tridodecylamine (TDA) dissolved in different two different acetates (ethyl acetate and propyl acetate), two different alcohols (1-octanol and 1decanol), and two different ketones (2-heptanone and 2-octanone), as well as single solvents. The C* ), experimental results of batch extraction experiments are reported as distribution coefficients, (KD = CPA PA loading factors, Z, and extraction efficiency, E. All measurements were carried out at 298.15 K. The highest distribution coefficient has been obtained by 1-octanol value of 4.121 and its extraction efficiency is 80%. Linear Solvation Energy Relationship (LSER) model has been applied to the experimental data with good regression coefficient, R2:0.90. Model results are close to experimental results. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Pyridine carboxylic acids and their derivatives are attracting considerable attention for their presence in many natural products. Especially, they are used in medicinal chemists, owing to the many of physiological facilities displayed by the natural and many synthetic derivatives [1]. They are also important from the industrial point of view; for example, in nuclear reactor decontamination, where the low oxidation state metal ion (LOMI) decontamination process uses V(II)/ V(III) picolinic acid complexes in the decontamination solutions [5,6]. 2-Pyridinecarboxylic acid, also known as picolinic acid, contains a carboxylic group in the ortho-position to the nitrogen in the pyridine ring, acting as a bidentate ligand by (N, COO−) coordination. It forms in the body as an intermediate in the tryptophan degradation pathway and it is an approved food supplement [2]. Picolinic acid contains two active groups: a carboxyl group and a pyridinic nitrogen atom, therefore its aqueous solutions are weakly acidic. When the product must be concentrated from an aqueous solution, existing fermentation technologies for large-scale production of common chemical feedstocks are not ready for action with
⁎ Corresponding author. Tel.: +90 212 4441997 5274; fax: +90 212 8675066. E-mail address: [email protected] (H. Uslu). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.10.009
traditional processes. These processes are expensive because of highenergy consumption occupied. To improve the biological production of picolinic acid and its derivatives by fermentation, it is necessary to develop new methods that reduce the charge of the recovery steps. Therefore, a realistic and more capable method using cheap and environment friendly is still of attention [3,4]. Physical extraction with pure organic solvents not containing amine- and phosphorus-structured extractant has been verified unsuitable for the recovery of organic acids. Because organic acids have high affinity to water, it gives low distribution coefficients. The pure diluents do not extract the solute, while the modifier influences the extracting power of the amine. When the amine salts with carboxylic acids are slightly soluble in the aqueous phase, a vital role of the modifier is to improve the solubility of the salts in the extracted phase [7]. Reactive liquid–liquid extraction of the acid by a suitable extractant has been found to be a promising alternative to conventional processes. Several authors [8–10] have studied the recovery of carboxylic acids by liquid–liquid extraction with aliphatic tertiary amines dissolved in organic diluents. The behavior and base strength of various amine types and classes in the reactive extraction of hydrochloric acid in toluene diluents have been investigated [11]. It is noteworthy in a study that the base strength increased in the order: tertiary amine N secondary amine N primary amine. Extraction of carboxyl acids by using some aliphatic amines and gel have been used successfully and some of reports could be found in the literature hitherto [12–28].
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140
where a denotes the activity. Replacing the activities by the products of molalities and molal activity coefficients, γ, gives Eq. (3).
Picolinic Acid O
C
O
O
H
C
H O
HO
C
Structure I
O K=
Structure II
Structure III
Table 1 Results of physical extraction of picolinic acid with pure solvents.
Ketones Alcohols
ð3Þ
3
In Eq. (3), mHA is the molality of acid, m*R3N is the molality of amine, γPA is the molal activity coefficient of acid, γ*R3N is the molal activity coefficient of amine, γ*(PA).(R3N) is the molal the activity coefficient of the complex, m*(PA).(R3N) is the molality of complex. The loading of the extractant (Z) is defined as the total concentration of acid in the organic phase divided by the total concentration of amine in the organic phase [8]. The expression for Z can be written in the form
Fig. 1. Structures of picolinic acid.
Esters
m*ðPAÞ:ðR NÞ ⋅γ*ðPAÞ:ðR NÞ 3 3 ðmPA ⋅γPA Þ⋅ m*R N ⋅γ*R N 3
N
N
N
135
T
T
Z = CPA = CTDA :
Solvents
pHaq.
C⁎PA (mol dm− 3)
KD
E
Ethyl acetate Propyl acetate 2-Heptanone 2-Octanone 1-Octanol 1-Decanol
3.154 3.131 3.097 3.084 3.084 3.126
0.044 0.057 0.012 0.032 0.062 0.057
0.059 0.077 0.016 0.041 0.084 0.077
5.565 7.145 1.535 3.981 7.751 7.145
ð4Þ
⁎ is total concentration of acid in the organic phase, In Eq. (4), CPA ⁎ mol/L and CTDA is the total concentration of amine in the organic phase. The partitioning coefficients, KD, for picolinic acid extracted from water into the organic phase were determined by T
KD = CPA = CPA :
ð5Þ
The efficiency of extraction, E, is expressed as 2. Theory
E = ½1−ðCPA = CPA0 Þ:100
The extraction of picolinic acid (HA) with tridodecylamine (R3N) can be described by the following reaction [8,10].
where CPA is the concentration of acid in the aqueous phase after extraction and CPA0 is the initial concentration of acid in the aqueous phase.
ð1Þ
PA + R3 N↔ðPAÞ:ðR3 NÞ
In Eq. (1) PA represents the nondissociated part of the acid present in the aqueous phase and the organic phase species are marked with an asterisk (*). Reaction (1) can be characterized by the overall thermodynamic extraction constant K. a*ðPAÞ:ðR
3 NÞ
aPA ⋅a*R
ð2Þ
3N
3. Materials and experimental procedure 3.1. Materials TDA (M = 521.98 g mol−1) (purity N 99 wt.%), picolinic acid (purity N 98 wt.%) and the solvents were purchased from Merck Co., (Darmstadt, Germany). All chemicals were used without further purification. Alcohols (1-octanol and 1-decanol), ketones (2-heptanones and 2-octanone), and esters (ethyl acetate and propyl acetate) (purities N 99 wt.%) were supplied from Merck and Fluka.
0,090 1-Octanol
0,080
Propyl Acetate
1-Decanol
0,070
Distribution Coefficients
K=
ð6Þ
0,060
Ethyl Acetate
0,050 2-Octanone
0,040 0,030 0,020
2-Heptanone
0,010 0,000 Fig. 2. Distribution coefficients of picolinic acid between water and solvents used in this study.
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Table 2 Results of extraction of picolinic acid with TDA + ester systems. Solvents (esters)
C⁎TDA (mol dm− 3)
pHaq.
C⁎PA (mol dm− 3)
KD
Z
E
Ethyl acetate
0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785
3.772 3.840 3.917 3.923 3.926 3.588 3.714 3.762 3.767 3.775 3.703 3.887 4.107 4.334 4.349 3.742 3.762 4.108 4.217 4.299 3.550 3.632 3.820 3.823 3.826 3.504 3.682 3.713 3.768 3.771
0.183 0.292 0.345 0.357 0.370 0.140 0.200 0.243 0.254 0.264 0.160 0.336 0.492 0.617 0.641 0.214 0.300 0.478 0.522 0.564 0.138 0.210 0.269 0.304 0.316 0.082 0.154 0.221 0.241 0.259
0.298 0.579 0.764 0.811 0.868 0.214 0.334 0.440 0.467 0.495 0.252 0.729 1.612 3.423 4.121 0.366 0.602 1.498 1.902 2.419 0.210 0.358 0.510 0.617 0.657 0.115 0.239 0.384 0.433 0.482
1.164 0.931 0.733 0.568 0.472 0.894 0.636 0.517 0.404 0.336 1.020 1.070 1.044 0.982 0.817 1.361 0.954 1.015 0.832 0.718 0.881 0.669 0.572 0.484 0.403 0.522 0.489 0.470 0.383 0.330
22.934 36.673 43.301 44.775 46.472 17.602 25.052 30.545 31.823 33.097 20.096 42.164 61.720 77.393 80.472 26.811 37.592 59.961 65.546 70.749 17.364 26.343 33.791 38.166 39.654 10.291 19.266 27.747 30.196 32.518
Propyl acetate
1-Octanol
1-Decanol
2-Heptanone
2-Octanone
3.2. Experimental procedure
4. Results and discussion
Extraction experiments involve shaking equal volumes (20 ml) of aqueous and organic phases for 6 h in a temperature controlled shaker (GFL) at 25 °C and 40 rpm speed, followed by settling of the mixture for at least 2 h at the same temperature in incubator. 6 h was found as sufficient time for the attainment of equilibrium in preliminary tests. Aqueous phase pH was measured by a (Mettler Toledo) pH meter. Aqueous solutions of picolinic acid have pH values in the range from 3.084 to 4.349. Aqueous-phase acid concentration was determined by titration of 0.1 N NaOH. Relative uncertainty of aqueous phase determination was not exceeding ±3%. The acid content in the organic phase was determined with a mass balance.
The picolinic acid monomer can exist in three conformations. From the relative energies gathered (Fig. 1), it is evident that the structure of picolinic acid is the most stable one which able to make a complex with amine via intramolecular hydrogen bond occurred between carboxylic acid and TDA (COOH⋯N). The other two are less stable by 3.50 and 3.67 kcal/mol, respectively, whereas structure I is the most stable one with 0.00 energy difference [28]. The physical extraction of picolinic acid was studied for better understanding of the amine effect on picolinic acid (reactive extraction). Table 1 presents and Fig. 2 shows the extraction of picolinic acid by pure solvents without TDA. With the help of pure 1-octanol the highest
4,5
Distribution Coefficients
4,0 3,5 3,0 2,5 2,0 1,5 1,0 0,5 0,0 0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 3. Variation of distribution coefficients with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140
137
1,4 1,3 1,2
Loading Factor
1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 4. Variation of loading factor with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
90,000 80,000
Extraction Efficiency
70,000 60,000 50,000 40,000 30,000 20,000 10,000 0,000 0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Concentration of TDA (mol/L) Fig. 5. Variation of extraction efficiency with concentration of TDA in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
4,0000
Distribution Coefficients
3,5000 3,0000 2,5000 2,0000 1,5000 1,0000 0,5000 3,4000
3,5000
3,6000
3,7000
3,8000
3,9000
4,0000
4,1000
4,2000
4,3000
4,4000
pH Fig. 6. Variation of distribution coefficiency with pH in different individual diluting solvents: ■, 1-octanol; □, 1-decanol; ▲, 2-heptanone; ▬, 2-octanone; ○, ethyl acetate; ●, propyl acetate.
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Fig. 7. FTIR analysis of organic phase and TDA.
extraction degree was raised to 7.751% of picolinic acid in aqueous phase to organic phase. In the diluents categories, alcohols more dominated than others did since they have high polarity. The extraction of picolinic acid by TDA dissolved in alcohols (1-octanol and 1-decanol), ketones (2heptanone and 2-octanone), and esters (ethyl acetate and propyl acetate) was studied. Results of the equilibrium data on the reactive extraction of picolinic acid from aqueous phase to organic phase are presented in Table 2. The prepared constant concentrations of TDA in various solvents were between 0.157 mol dm−3 and 0.785 mol dm−3. The picolinic acid concentration in the initial aqueous phase was 0.797 mol dm−3. According to Table 2 and Fig. 3, the distribution coefficient for picolinic acid extraction with TDA was obtained obviously by the following orders: In alcohols: 1-octanol N 1-decanol In esters: ethyl acetate N propyl acetate In ketones: 2-heptanone N 2-octanone.
As has been obviously seen from Fig. 4 in contrast to action of KD values, the loading factors show gradual decrease when increasing amine concentration in the organic phase. In low concentrations (interval 0.157 mol dm−3–0.471 mol dm−3) over loadings (Z N 1) were observed. As per Wasewar et al. [21]. If 1 N Z N 0.5 complex formation (2 acid molecules + 1 amine molecule) ½TDA : ACID + ½ACID↔½TDA : 2ACIDS If Z N 1 (3 acid molecules + 1 amine molecule) can be considered ½TDA : 2ACID + ½ACID↔½TDA : 3ACIDS: Fig. 5 demonstrates the extraction efficiency of TDA–diluents mixture changes when increasing initial concentration of TDA in organic phase. The highest extraction efficiency of picolinic acid has been found as 80.472% using 1-octanol at 0.785 mol dm−3 initial
Table 3 Solvatochromic parameters for alcohols [32,35,36]. Solvents
π*
δ
β
α
Octan-1-ol Decan-1-ol Propyl acetate Ethyl acetate 2-Heptanone
0.40 0.40 0.53 0.55 0.61
0 0 0 0 0
0.81 0.81 0.45 0.45 0.48
0.77 0.72 0 0 0
Table 4 Results of regression coefficient for LSER equation. Coefficients
K0D
s
d
b
a
R2
− 1.337
− 4.451
0
6.842
2.301
0.90
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140 Table 5 KD values for the experimental and LSER model. Solvents (ketones)
C⁎TDA (mol dm− 3)
KD
KDmodel
2-Heptanone
0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785 0.157 0.314 0.471 0.628 0.785
0.210 0.358 0.510 0.617 0.657 0.252 0.729 1.612 3.423 4.121 0.366 0.602 1.498 1.902 2.419 0.298 0.579 0.764 0.811 0.868 0.214 0.334 0.440 0.467 0.495
0.225 0.375 0.468 0.641 0.644 0.266 0.741 1.645 3.877 3.997 0.372 0.605 1.559 2.055 2.657 0.325 0.566 0.771 0.955 0.965 0.311 0.335 0.554 0.565 0.585
Octanol
Decanol
Ethyl acetate
Propyl acetate
concentration of TDA. The acid concentration in the organic phase at equilibrium C⁎PA increases from 0.082 mol dm−3 to 0.641 mol dm−3 with increasing concentration of TDA from 0.157 mol dm−3 to 0.785 mol dm−3. Distribution coefficient has increased from 0.016 to 4.121 with increasing initial TDA concentration among the all diluents used in this study in Fig. 6. Obviously, as can be seen from Table 2, the increase of amine concentration brings about gradual increase of extraction efficiency. At 0.785 mol dm−3, the maximum values of 80.472% and 70.749% of the picolinic acid (for two diluents) are extracted with 1-octanol and 1-decanol, respectively. The equilibrium data about distribution of picolinic acid between water and TDA dissolved in 2-heptanone and 2-octanone were presented in Table 2. It was found that the extraction power of TDA is more effective in the presence of 2-heptanone than 2-octanone. The most characteristic bands in the FTIR spectra of organic phase (bottom, after extraction) and amine (top, before extraction) (Fig. 7)
139
should be mentioned that correspond to the stretching vibrations of carbonyl group in the expected regions. It is often used here to correlate the IR spectrum with the carboxylate structures by using the difference between the asymmetric and symmetric carboxylate stretches. This value has been observed at 1609 cm−1 for stretching vibrations of carbonyl group. In the spectral range over 3000 cm−1, at 3350 cm−1, O–H stretch has occurred at organic phase. Tridodecylamine is a tertiary amine so that N–H stretch has not been observed at 3300–3000 cm−1, or an N–H wag. The C–N stretch has been seen at 1378 cm−1 (non-aromatic) at amine. A LSER approach was introduced by Kamlet and Taft [29] and then improved by Abraham [30]. It characterizes solvation effects in terms of nonspecific and hydrogen bonding interactions. Thus, a solvation property of interest (XYZ) for an organic solute is modeled by a linear solvation energy relationship of the form [31] 0
XYZ = XYZ + s π* + sdδ + bβ + aα:
ð7Þ
In Eq. (7), π* and δ are the solvatochromic parameters that measure dipole + dipole and dipole + induced dipole interactions, respectively. The solvatochromic parameter α scale of solvent HBD (hydrogen-bond donor) acidities describes the ability of the solvent to donate a proton in a solvent to solute hydrogen bond. The β scale of HBA (hydrogen-bond acceptor) basicities provides a measure of the solvent's ability to accept a proton (donate an electron pair) in a solute to solvent hydrogen bond, respectively. The coefficients s, d, a and b include the properties of solute coming from regression [32]. As mentioned in Uslu's previous studies [33,34] the general form of LSER (Eq. (5)) can be rearranged to predict distribution coefficient of reactive extraction systems, 0
ln KD = ln KD + sðπ* + dδÞ + bβ + aα:
The solvatochromic parameters (π*, δ, β, and α) for each solvent were taken from the literature and shown in Table 3. The results of the regression of data obtained from experimental data according to Eq. (8) give other coefficients (K0D, s, d, a and b) and their values were presented in Table 4. These values give us the new equation to predict distribution coefficients for these extraction systems and comparison of KD values between calculated and experimental was given in Table 5. It has been seen clearly from Fig. 8 that the predicted values of KD are close to experimental data. This situation shows that the LSER
4.5 4
KD Experimental
3.5 3 2.5 2 1.5 1 0.5 0
0
1
2
ð8Þ
3
4
KD LSER model Fig. 8. Comparison of KD values between experimental and LSER model.
5
140
A.F. Tuyun, H. Uslu / Desalination 268 (2011) 134–140
model is in good agreement with experimental data in these conditions. For the suitability of the data, the root-mean-square deviation (RMSD) values are calculated from the difference between the experimental data and the predictions of the LSER model, according to the following equation: RMSD =
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 n ∑ KD −KDmodel N i=1
ð9Þ
where KD, is the experimental distribution coefficient and Kmodel is the D calculated distribution coefficient. N is the number of experimental data. The RMSD value of LSER model is determined to be 0.89. The RMSD value shows that all predicted distribution coefficients agree well with each other, and also the agreements between predictions and measurements are acceptable, considering experimental uncertainty. 5. Conclusion The reactive extraction of picolinic acid by using TDA dissolved in three diluents was investigated. The distribution coefficients, loading factors, and extraction efficiencies were obtained for this extraction system. The highest synergistic extraction efficiency was found for TDA + 1-octanol extractant system with KD value of 4.121. Polar diluents have been shown to be more convenient diluents than inert ones (nonpolar), due to their higher distribution. However, active polar and proton-donating diluents such as alcohols have been shown to be the most suitable diluents for amines because they give the highest distributions resulting from the formation of solvates through specific hydrogen bonding between the proton of the diluents and the acid–amine complex. The employment of the reactive extraction method on recovery steps after production of acids provides us the solutions of some problems such as high-energy consumption, tedious work up procedures, cost, and environment problems. References [1] K.A. Idriss, M.S. Saleh, H. Sedaira, M.M. Seleim, E.Y. Hashem, Solution equilibria and stability of the complexes of pyridinecarboxylic acids — complexation reaction of mercury(II) with 2-hydroxynicotinic acid, Monatsh. Chem. 122 (1991) 507–520. [2] RA. Anderson, Chromium in the prevention and control of diabetes, Diabetes Metab. 26 (2000) 22. [3] L.R. Wang, Y. Fang, UV-Raman study and theoretical analogue of picolinic acid in aqueous solution, J. Molec. Spect. 234 (2005) 137–142. [4] J.M. González-Sáiz, M.A. Fernández-Torroba, C. Pizarro, Application of weakly basic copolymer polyacrylamide (acrylamide-co-N,N,'-dimethylaminoethyl methacrylate) gels in the recovery of citric acid, Euro. Poly. J. 33 (1997) 475–485. [5] C.G. Pope, E. Matijecic, R.C. Pate, Adsorption of nicotinic, picolinic, and dipicolinic acids on monodispersed sols of alpha-Fe2O3 and Cr(OH)3, J. Colloid Interface Sci. 80 (1981) 74–83. [6] A.M. Lannon, A.G. Lappin, M.G. Segal, Electron-transfer reactions of tris (picolinato) vanadate(II), a LOMI reagent, Inorg. Chem. 23 (1984) 4167. [7] D.S. Yankov, J.R. Molinier, G.D. Kyuchoukov, Extraction of tartaric acid by trioctylamine, Bulg. Chem. Comm. 31 (1999) 446. [8] V. Bizek, J. Horacek, R. Rericha, M. Kousova, Amine extraction of hydroxycarboxylic acids 1. Extraction of citric-acid with 1-octanol n-heptane solutions of trialkylamine, Ind. Eng. Chem. Res. 31 (1992) 1554–1562. [9] R.S. Juang, R.H. Huang, Equilibrium studies on reactive extraction of lactic acid with an amine extractant, Chem. Eng. J. 65 (1997) 47–53. [10] A.S. Kertes, C.J. King, Extraction chemistry of fermentation product carboxylic acids, J. Biotechnol. Bioeng. 28 (1986) 269–282. [11] R.R. Grinstead, Proc. of the Int. Solvent Extraction Conf. North-Holland, Amsterdam, 1967. [12] G. Kyuchoukov, A. Labbaci, J. Albet, J. Molinier, Simultaneous influence of active and “inert” diluents on the extraction of lactic acid by means of tri-n-octylamine (TOA) and tri-iso-octylamine (TIOA), Ind. Eng. Chem. Res. 45 (2006) 503–510.
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Glossary Symbols and abbreviations
TDA: Tridodecylamine HA: Picolinic acid KD: Distribution coefficient Z: Loading factor CPA: Picolinic acid concentration [mol.dm-3] CPA0: Initial concentration of picolinic acid [mol dm− 3] E: Extraction efficiency Aq: Aqueous phase *: Organic phase